Logo: Ornament and credit cards (Tom Grill-Corbis)
An estimated $110 billion worth of gift cards were sold this year in the United States, according to research from CEB TowerGroup. That's a 10% increase over 2011.

In other words, you might very well be among the millions of Americans finding  promissory plastic under the tree.

But suppose you unwrap a 'meh' or downright unusable gift card -- a steakhouse scrip although you've gone vegan, say, or credit at a movie theater chain that doesn't operate in your city?

Here's what you do: You smile, thank the kind giver and then trade the card for cash on Dec. 26 -- Gift Card Exchange Day.

Luke Knowles, founder of the secondary market aggregator site Gift Card Granny, created Gift Card Exchange Day for two reasons:

  • Online search activity for "exchange gift cards" peaks the day after Christmas, so clearly the interest is there.
  • Secondary market companies like  Cardpool and Plastic Jungle sold an awful lot of cards during the holiday season. Now they're willing to pay top dollar for fresh supplies.
The process is pretty simple. Visit the Gift Card Exchange Day website and find the name of the merchant in the dropdown box under "Sell a Gift Card." Enter the card value and you'll get instant offers from multiple resellers. Choose the one you want and you'll be redirected to that company's site to finish the deal.

Some sites offer more if you take an Amazon.com gift card instead of cash. For example, a $50 Target gift card recently garnered offers of $44 to $47.50 in cash and $47.88 to $49.88 in Amazon credit.

Some extra cash

Another reason to sell gift cards: You'd rather have the money. Students, recent grads, the under- or unemployed -- you know what I'm talking about. It was very kind of your parents to give you a $50 iTunes card or for your boss to hand over $25 worth of Sephora scrip, but a little folding green would be more useful right now.

This is especially true if you overdid the holiday shopping and are anticipating scary credit card bills in January.

"I'd rather have the money" may sound crass. But look at it this way: Once you receive a gift it's yours to do with as you please.

You don't have to keep that reindeer sweater, once you've modeled it for the well-meaning relative who gave it to you. Nor do you have to spend that bookstore gift card if you could really use the money.
That's why I spent a few minutes last Dec. 26 looking for the best offers on two gift cards ($25 and $50) that I received but didn't want to keep. These turned into $63.79 worth of Amazon.com scrip, which arrived in less than a week.

Sure, you could sell the gift cards yourself: at work, to friends, to strangers on Craigslist. You might have a kind friend or relative who'd pay full face value. Or you could hold on to the plastic until someone's birthday or anniversary rolls around.

The first way is more work. The second isn't likely. The third risks "spillage," the industry term for lost or forgotten cards. Besides, I can't imagine you’d do much better than $49.88 in Amazon scrip.

P.S. Don't forget to write your thank-you notes.

Have you ever sold a gift card?

More on MSN Money: